Researchers Zero In on Cyanide as Cause of Foal Loss Syndrome

Researchers at the University of Kentucky Gluck Equine Center have made significant progress in their quest to find the cause of the Mare Reproductive Loss Syndrome.

According to reports presented Thursday during an informational forum at Keeneland, black cherry trees located in close proximity to horse pastures are the primary source of the cyanide that was detected in tests of dead foals and fetuses from mares that aborted.

While it is unknown how the mares ingested the cyanide, the hypothesis being pursued by the researchers centers on Eastern tent caterpillars ingesting leaves from black cherry trees.

Dr. M. Scott Smith, dean of the UK College of Agriculture, emphasized that the black cherry tree-cyanide link had materialized in the 24-hour period prior to Thursday's meeting. He said other hypotheses are being pursued, but that the evidence is pointing toward the cyanide as the cause of the problem that has had a negative impact on the horse breeding industry. Smith said the black cherry tree-eastern tent caterpillar theory has not met standards for scientific study.

"We believe that cyanide poisoning is a primary agent in both late term abortions and early fetal loss problems," Smith said. "The wild, black cherry trees are a likely source for this cyanide and the eastern tent caterpillar is a leading candidate to be either directly or indirectly involved in carrying this to horses."

Tobin explained that black cherry trees contain substances that produce sugars, which under the right conditions, produce cyanide. "It is well known that wilted leaves or broken branches from a black cherry tree are lethal to cattle and sheep," Tobin said.

Tobin said eastern tent caterpillar are highly adapted to black cherry trees and are immune to the cyanide produced by the trees. Tobin said the field studies undertaken by researchers indicated that tent caterpillar had stripped black cherry trees of their leaves by April 25, when the first indications of a problem with mares and foals materialized.

"The toxin (that caused Mare Reproductive Loss Syndrome) is cyanide and the source is the black cherry tree located in close proximity to pastures," Tobin said. "Precisely how the delivery to the mare occurred is unclear."

Based on the evidence presented so far the researchers were concluding that the cyanide levels were insufficient to cause clinical signs in the mares but to cause problems for the fetuses.